This invention relates to a process for recovering uranium and hydrofluoric acid from a waste liquor containing uranium and fluorine. More particularly, it relates to a process for efficiently and separately recovering uranium and fluorine from a waste liquor produced in a step of converting natural or depleted uranium into uranium hexafluoride or in a step of reconverting uranium hexafluoride from enriched or depleted uranium into uranium oxide.
Conventional processes for refining uranium may be broadly classified into dry and wet ones. Although the dry process produces little waste liquor, it costs a great deal since it requires a complicated apparatus and delicate temperature control. One the other hand, the wet process involves reactions which can proceed uniformly. Thus it can be readily carried out with a simple apparatus without any trouble of corrosion. However the principle of the wet process makes it unavoidable that a large amount of waste liquor is produced thereby. The waste liquor frequently contains uranium and fluorine. For example, in the case of a PNC process comprising the procedures as shown in FIG. 1 (see Journal of the Mining and Metallurgical Institute of Japan, 99,523(1983)), an aqueous solution of uranous chloride produced by electrolytic reduction is reacted with hydrofluoric acid in a fluorinating precipitation step, and the reaction product, i.e., uranium tetrafluoride crystals, is drawn from an outlet at the bottom of a reaction tank as a thick slurry, while the waste liquor containing uranium and fluoride is produced as an overflow solution from the top of the tank.
This waste liquor containing uranium and fluorine should be treated and discharged. A conventional method therefor is solid-liquid separation by neutralizing precipitation with the use of slaked lime.
However a cake, which is obtained by the above-mentioned solid-liquid separation by neutralizing precipitation with the use of slaked lime and mainly comprises calcium fluoride, contains radioactive uranium compounds. Therefore, this cake should be sealed in a drum and stored as a radioactive solid waste. Furthermore there is another problem that, if sulfate ion is contained in the waste liquor, the slaked lime would react with the sulfate ion to form a large amount of water-insoluble gypsum in the precipitation step, which brings about an extremely large increase in the amount of the cake to be stored.